1. Field of the Invention
The present invention relates to a method of manufacturing a wiring substrate, and to an ejection head and image forming apparatus, and more particularly, to electrical wiring technology in an ejection head which ejects liquid from nozzles.
2. Description of the Related Art
In an inkjet recording apparatus, it is essential to provide a large number of nozzles ejecting liquid and to arrange these nozzles at high density, in order to achieve high-speed recording and high quality of the recorded image, and hence ejection heads having a large number of nozzles arranged in a matrix configuration have been proposed. If the nozzles are arranged at high density, then this means that the ejection force generating elements, which are provided to respectively correspond to the nozzles, are also arranged at high density, and the wiring conductors transmitting drive signals to be applied to the ejection force generating elements are also arranged at high density. If the wiring density of the wiring conductors is increased, then the width and surface area of the wiring conductors decrease and the adhesive force (bonding force) decreases between the wiring conductors and the substrate on which the wiring conductors are formed, so that a problem of reduced bonding reliability arises. Therefore, various methods have been proposed for ensuring a prescribed adhesive force between the substrate and the wiring conductors, when forming a wiring pattern comprising the wiring conductors on the substrate.
Japanese Patent Application Publication No. 2001-320150 discloses that a wiring pattern is transferred onto the surface of a substrate by using a stamper having an inverse pattern of recesses and projections with respect to the wiring pattern, and the wiring pattern having grooves of 30 μm width or less is formed.
Japanese Patent Application Publication No. 2004-356255 discloses that a metal mold having a prescribed pattern is manufactured by performing ultrafine mold processing in a metal material, and a non-conductive substrate having a groove-shaped pattern is manufactured by transferring this mold, whereupon conductive material is injected into the groove-shaped pattern formed in the substrate in such a manner that wires are formed on the substrate.
In general, as the method for forming wiring conductors in a groove-shaped pattern formed on a substrate, it is common to use a method for filling a conductive paste into the groove-shaped pattern, since the forming procedure is simple. If wiring conductors are formed by filling a conductive paste into the groove-shaped pattern, then the impedance (specific resistance) of the wiring conductors is ten times or greater than the impedance when wiring conductors are formed by a plating method, or the like. The wiring conductors (the wiring pattern) having a large wiring impedance is problematic in that it degrades the electrical characteristics of the transmitted signal (noise tolerance characteristics, frequency characteristics, and the like).
Here, to give examples of the relationship between the type of wiring material and the specific resistance (unit: Ω·cm), if pure copper is used as the wiring material, then the specific resistance is 1.68 μΩ·cm. Copper wiring formed by electrodeposition from an acidic bath of low organic concentration has the specific resistance of 1.72 μΩ·cm, and copper wiring formed by electrodeposition from a standard acidic bath has the specific resistance of 1.78 μΩ·cm. If an electroless copper plating film is used as the wiring material, then the specific resistance is 2 μΩ·cm to 3 μΩ·cm. On the other hand, if a conductive paste (conductive copper paste) is used as the wiring material, then the specific resistance is 30 μΩ·cm to 40 μΩ·cm.
In the wire formation disclosed in Japanese Patent Application Publication No. 2001-320150, a step is required for removing the conductive film between adjacent wires (on the projecting sections formed on the substrate). If polishing is used as the method for removing the conductive film, then the end sections of the substrate become dulled, and it is difficult to achieve uniform polishing of the substrate, especially in the case of a substrate having a large surface area. In particular, if wiring conductors (a wiring pattern) are formed on a structure having a complicated shape, then it is difficult to remove the unwanted conductive film in a uniform manner by polishing. Furthermore, it is also necessary to dispose of sludge generated during the polishing.
In the wire formation disclosed in Japanese Patent Application Publication No. 2004-356255, if an inkjet head, or the like, is used when injecting the conductive material into the groove-shaped pattern, then a solvent is required in which the conductive material can be contained in order to be ejected from the inkjet head. Consequently, the amount of conductive material injected into the groove-shaped pattern in each operation is reduced, and in order to achieve prescribed wiring impedance, it is necessary to repeat the injection of the conductive material into the groove-shaped pattern, a plurality of times.